Several methods are earlier known for treatment of difficult wounds, such as infected wounds, diabetes wound, pressure sore or deep wounds.
Drainage of for instance operation wounds or other liquid discharging wounds with the aid of negative pressure is a standard treatment that has been used for decades. An example of a manual suction pump for said use is described in U.S. Pat. No. 3,742,952.
In said publication is described a pump in form of an elastically compressible body of an open-cell foam, preferably a polyurethane foam. Said body also serves as a canister for exudate drained from the wound. It is stated that the pump has a capacity to hold a negative pressure of 15-80 mmHg more than 48 hours. A drainage tube is arranged with a perforated end part in the wound cavity and via tube connected to the pump.
A similar device is described in U.S. Pat. No. 4,525,166. In the description of said publication is specifically stated that the negative pressure in addition to drain wound fluids from the wound also presses the edges of the wound together, thereby stimulating rapid tissue granulation and healing of the wound. The two mentioned publication thus teach that vacuum treatment of wounds stimulates the healing of the wounds.
The terms vacuum treatment, treatment at a reduced pressure and treatment with negative pressure are alternatively used in the literature. When using any of this terms in the present description the terms always concern treatment at pressure below normal atmospheric pressure.
Treatment of deep wounds have earlier also been performed by adding an irrigation liquid to the wound and then draining the injected liquid and pus and bacteria present in the wound before the irrigation. Examples of such devices are described in U.S. Pat. No. 5,385,494 and U.S. Pat. No. 4,382,441.
Extensive investigations of the effect of continuous and intermittent treatment of wounds under negative pressure, i.e. pressure below atmospheric pressure, were performed in the 1980's at Russian institutes. One was able to establish that difficult and normally slow-healing wounds healed considerably faster with the aid of vacuum treatment compared with conventional treatment.
One was inter alia also able to show that treatment at a reduced pressure provides a significant antibacterial effect. Said Russian investigations are described in several articles in the Russian medical journal Vestnik Khirurgii. The relevant articles from said journal are:                1) Kostiuchenok et al, September 1986, pages 18-21.        2) Davydov et al, September 1986, pages 66-70.        3) Usupov et al, April 1987, pages 42-45.        4) Davydov et al, Oktober 1988, pages 48-52.        5) Davydov et al, Februari 1991, pages 132-135.        
In an article by Chariker et al in the journal Contemporary Surgery, No. 34, June 1989 is stated that vacuum treatment stimulate tissue granulation and contraction of wounds, which with conventional treatment are very difficult to heal.
Vacuum treatment of wounds is also described in U.S. Pat. Nos. 4,969,880, 5,645,081, 5,636,643, 6,855,135 B2 and WO 2006/025848 A2.
Hitherto known devices for vacuum treatment of wounds are not satisfactory in every respect. For instance U.S. Pat. No. 5,645,081 describes a wound pad in form of an open-cell foam. It is believed that cell growth are stimulated when tissue can grow into the pores of the foam but there is also a risk that the formed tissue fasten in the pores and is damaged when the pad is removed from the wound. There is a demand to improve wound pads for use in severe and deep wounds.
Disclosure of Invention
By means of the present invention an improved device of the type mentioned in the introduction has been achieved. The device in accordance with the invention is characterized in that the wound pad consist of an open-cell polyurethane foam which is fully impregnated with a soft hydrophobic silicone gel, and that the foam has a hardness of 1.0-6.0 kPa measured according to ISO 3386-1 at 40% compression.
According to an embodiment the invention is further characterized in that the density of the foam is 20-40 kg/m3, and preferably 25-35 kg/m3 measured according to ISO 845.
According to an embodiment the invention is characterized in that the foam at 25% elongation has a wet elasticity higher than 6 kPa and a dry elasticity higher than 13 kPa measured according to a method described in Appendix A.
According to an embodiment the invention is characterized in that the silicone gel is homogeneously distributed over the cross-section of the pad of open-cell foam.
According to an embodiment of the invention the open-cell foam is fully impregnated with silicone gel as approved by observing photos taken with an Electron Probe Micro Analyser with Energy Dispersive Spectrometer (EPMA/EDS), such as JEOL, model JXA-8600.
According to an embodiment the invention is further characterized in that the cell diameter is between 500-1800 μm, such as between 1100-1500 μm measured according to Visiocell SS-T.013.4E. Foam of this type is sold by for instance the Belgian firm Recticel.
The inventive concept is the specific wound pad intended to be arranged in a wound cavity. The invention also concerns a device for treatment of wounds without using reduced pressure. According to a modified embodiment, i.e. without using reduced pressure, a device comprising a wound pad to be arranged in the wound cavity, an absorbent member for collecting exudate from a wound and a sealing covering the wound, said wound pad and said absorbent member is characterized in that the wound pad consist of an open-cell polyurethane foam which is fully impregnated with a soft hydrophobic silicone gel, and that the foam has a hardness of 1.0-6.0 kPa measured according to ISO 3386-1 at 40% compression.
Said foam is according to an embodiment further characterized in that the cell diameter is between 500-1800 μm, and preferably 1100-1500 μm measured according to Visiocell SS-T.013.4E.
The present invention also concerns a method for manufacturing the wound pad. The method according to the invention is characterized in that silicone gel in uncured state is applied on one side of a web of said foam, that said web with the applied silicone gel is fed between two webs of process paper through a pair of press rolls, between which press rolls the foam with the applied silicone gel is squeezed for distributing the gel over the total cross section of the foam, that said two webs of process paper with excessive silicone gel from the foam web are removed from the foam web and that the foam web thereafter is heated for curing of the silicone gel.
According to an embodiment the method is further characterized in that the curing of the silicone gel is performed in a hot blast furnace at a temperature of about 100° C. during about 1-5 minutes, preferably about 3 minutes.
According to an embodiment the method is characterized in that the pressure between the press rolls is about 5 bar and that said pressure is adjustable for optimal impregnation and that control of full impregnation of the foam web is performed by inspecting the two webs of process paper, which both paper webs are coated with silicone gel when the foam web is fully impregnated.